SACRAMENTO, Calif. (AP) — California Gov. Gavin Newsom scrapped a $16 billion plan Thursday to build two giant water tunnels to reroute the state’s water system and instead directed state agencies to restart planning for a single tunnel.

The move came after $240 million has already been spent on the project championed by former Gov. Jerry Brown to divert water from the north to the state’s drier south.

Newsom had signaled the move in his February State of the State address. He made the change official when he asked state agencies to withdraw existing permit applications and start over.

“I do not support the twin tunnels. But we can build on the important work that’s already been done,” he has said.

Brown wanted to build two, 35-mile-long (55-kilometer-long) tunnels to divert water from the Sacramento River, the state’s largest river, to the San Francisco Bay Area, San Joaquin Valley and Southern California. Local water agencies were expected to foot the roughly $16 billion bill.

A single tunnel is expected to cost less, but officials haven’t yet set a price tag, said Erin Mellon, spokeswoman for the state Department of Water Resources. Nor has the state determined how much water would flow through a single tunnel.

California delivers water through a complex system of reservoirs, aqueducts and pumps known as the State Water Project, first started by Jerry Brown’s father, former Gov. Pat Brown.

Most of the state’s water comes from the Sacramento-San Joaquin River Delta, and the current system has become outdated as the state’s population has boomed to nearly 40 million people, with most living in the drier south.

Supporters of the tunnel project argue the pumping system, which is strong enough to change the direction of water flow, needs to be phased out. The Metropolitan Water District in Los Angeles has been the biggest supporter of the tunnels project. Many farmers back it, too.

But environmental groups argue the tunnels could suck too much water from the delta, harming species such as the delta smelt and chinook salmon. Some delta farmers also worry the project would harm their own water supply.

A smaller tunnel is likely to be just as long and take water from the same places, but it could be designed differently, said Karla Nemeth, director of the state Department of Water Resources.

State officials considered modifying the existing project but decided it was better to start fresh. That includes environmental reviews and doing more engineering and design work on the front end, which Nemeth said hadn’t been done in past versions of the project. It could take up to three years to develop all the new environmental documents.

Restore the Delta, a group opposed to the twin tunnels plan, praised Newsom’s decision to halt it. But Barbara Barrigan-Parrilla, the group’s executive director, said questions remain about whether one tunnel is necessary and how Newsom’s plan would affect water quality in Central Valley communities.

Kathryn Phillips of Sierra Club California said her organization does not support any tunnels. But she applauded an executive order Newsom signed Monday taking a big-picture approach to thinking about the state’s water needs and challenges from climate change. He directed several state agencies to assess how to best meet future water demands.

“I think all of that will add up to a place where we’ll find it doesn’t make sense to invest into the single tunnel,” Phillips said. “We’ve not been responsible in this state with how we use water.”

The Brown administration had previously considered downsizing the project to one tunnel as local water agencies balked at picking up the tab.